Printer drum gate latch assembly

ABSTRACT

A latch assembly useful in a high-speed printer for latching a hinged drum gate into alignment opposite to a hammer bank. The latch assembly is comprised of a roller mounted on the drum gate and rotatable about an axis extending through the hinge axis of the gate. The hammer bank frame carries a fixedly mounted bracket defining a slightly inclined entrance ramp leading to a receptacle having a precisely defined flat surface. A wedge plate, mounted for pivotal movement adjacent the bracket, is held in an unlatched position by a pivotable pawl when the roller is not present on the flat surface. As the roller rolls up the ramp on to the flat surface, it engages the pawl to release the wedge plate which, by spring action, is pivoted to a position with its wedge surface engaging said roller and locking it into said receptacle.

United States Patent Inventors George M. Hfl'amia Santa Ana; Harry Katt, Tarnnn, both of Calif. Appl. No. 850,052 l'ilcd Aug. 14, 1969 lmcnlctl Oct. 12, I971 Asiiigncc llllil Products Woodland Hills, Calif.

PRINTER DRUM GATE LATCH ASSEMBLY 8 Claims, 4 Drawing Figs.

2,528,864 11/1950 Curtiss,.lr

Primary ExaminerLouis G. Mancenc Assistant Examiner-J. A. Oliff An0rneyLindenberg, Freilich & Wasserman ABSTRACT: A latch assembly useful in a high-speed printer for latching a hinged drum gate into alignment opposite to a hammer bank. The latch assembly is comprised of a roller mounted on the drum gate and rotatable about an axis extending through the hinge axis of the gate. The hammer bank frame carries a fixedly mounted bracket defining a slightly inclined entrance ramp leading to a receptacle having a precisely defined flat surface. A wedge plate, mounted for pivotal movement adjacent the bracket, is held in an unlatched position by a pivotable pawl when the roller is not present on the flat surface. As the roller rolls up the ramp on to the flat surface, it engages the pawl to release the wedge plate which, by spring action, is pivoted to a position with its wedge surface engaging said roller and locking it into said receptacle.

PATENTEDncnzmn v 8.611.923

' SHEUBUFZ A TTORNE Y5 PRINTER DRUM GATE LATCH ASSEMBLY BACKGROUND OF THE INVENTION This invention relates to a latch assembly useful in a highspeed printing apparatus for aligning and latching a drum gate opposite to a hammer bank.

Many high-speed printers used in data processing systems employ a hammer bank positioned opposite to a rotating character drum. The hammer bank is comprised of a plurality of individually actuatable impact hammers and the character drum has raised characters formed on the peripheral surface thereof. Paper and printing ribbon webs pass between the hammer bank and the drum. In order to print a selected character in a particular position on the paper, the particular hammer disposed adjacent that position is energized when the selected character on the drum moves into alignment therewith. The hammer strikes the paper against the ribbon and drum character to thus print the character on the paper surface adjacent the ribbon. It will be appreciated that in order to achieve high-quality printing at high speeds, it is imperative that the drum and hammer bank be precisely positioned relative to one another.

In order to provide easy accessibility to the hammer and drum and to facilitate paper loading, it has become common practice to mount the drum on a frame or gate which is hinged relative to the hammer bank frame. Utilizing such a structural configuration, it is essential to provide some means for latching the gate in alignment with the hammer bank frame despite hinge wear.

Although several prior art latch arrangements have been designed to function in the aforedescribed environment, most have been deficient in at least certain respects. For example only, many such latches operate in a manner which requires a male latch member to slide over a surface into a receptacle in a female latch member. The sliding friction introduces wear which over a period of time, adversely affects precision alignment. Another undesirable feature of some proposed latches has been their inability to permit the hinged drum gate to be slammed closed. In utilizing such latches, it has been necessary to properly orient either one or both of the latch members prior to closing the drum gate, or else damage could result when the drum gate was slammed closed.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a latch assembly suitable for use in a highspeed printer which avoids the aforementioned defects of the prior art.

Briefly, in accordance with the present invention, a latch assembly is provided suitable for latching a hinged drum gate to a hammer bank frame in a high-speed impact printer. In the preferred embodiment of the invention, a roller is mounted on the drum gate for rotation about an axis extending through the hinge axis of the gate so as to permit the roller to roll, rather than slide, up an inclined entrance ramp of a bracket carried by the hammer bank frame. The ramp leads to a receptacle having a precisely located flat surface which in turn precisely locates the roller and drum gate. A wedge plate is mounted adjacent the receptacle to lock the roller therein. When the roller is not disposed in the receptacle, the wedge plate is held out of the way in an unlatched position by a pawl. Closing or slamming of the drum gate causes the roller to enter the receptacle and engage the pawl to in turn release the wedge plate to lock the roller in the receptacle. The wedge plate is spring urged into the locked position. Manual movement of a handle coupled to the wedge plate pivots the wedge plate from the locked position this releasing the roller and permitting the pawl to retain the wedge plate in its unlatched position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a high-speed impact printer incorporating a latch assembly in accordance with the present invention;

Flg. 2 is a top plan view of the printer of Flg. I;

FIG. 3 is a side view of a latch assembly in accordance with the present invention showing the latch assembly in an unlatched position; and

FIG. 4 is a side view showing the latch assembly of FIG. 3 in a latched position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now called to FIG. 1 of the drawing which illustrates the high-speed printing apparatus incorporating a latch assembly in accordance with the present'invention. The printing apparatus of FIG. 1 is basically comprised of a first frame 10 supporting a bank of individually actuatable impact hammers 12. The hammer tips 14 are disposed in horizontal alignment. The number of hammers normally provided is equal to the maximum number of characters it is desired to print in a single line. Thus, if it is desired to print lines having up to character positions, then it is normally necessary to provide 120 hammers.

The frame 10 also supports a paper drive tractor mechanism 16 driven by a motor 18. The printer apparatus of FIG. 1 normally prints on fanfolded edge perforated paper 20 which is pulled by the tractor mechanism 16 from the supply stack 20 past the hammer bank 12. The printer apparatus of FIG. 1 also includes a second frame or gate 30 which is hinged relative to the first frame 10 for movement about a substantially vertical hinge axis 31. The gate 30 supports a character drum 32 for rotation about its own axis. The drum is driven by a motor 33 and is supported behind a printing ribbon web 34 illustrated in FIG. 1. The circumferential surface of the drum is provided with a plurality (e.g. 120) of tracks, each track including a set of raised printing characters. Each track corresponds to a different character position in a line of print. The number of different characters in each track, of course, determines the number of different characters which can be printed in the corresponding position.

In the use of the apparatus of FIG. I, the gate 30 is moved from the open position illustrated to a closed position in which the printing ribbon web 34 is immediately opposed to the hammer bank 12. The paper is drawn by the tractor mechanism 16 from the stack 20 through the space the hammer bank 12 and printing ribbon 34. Printing is accomplished by incrementally moving the paper web, line by line, and by actuating each hammer when the appropriate character on the drum moves into alignment therewith to thus propel the hammer against the paper to urge the paper against the ribbon and drum.

From the foregoing description of the operation of the apparatus of FIG. 1, it will be readily recognized that in order to achieve high-quality printing, it is essential that the character drum be precisely positioned with respect to the hammer bank 12. On the assumption that the individual hammers can all be precisely positioned with respect to the frame 10 and that the drum axis can be precisely located with respect to the gate 30, it will be recognized that it is essential to precisely position the gate 30 with respect to the frame 10 when they are moved into operative relationship. The present invention is primarily directed to a latch assembly for latching together and precisely aligning the frames 10 and 30. I

More particularly, a latch assembly is provided in accordance with the present invention which is always properly oriented when the gate 30 is in the open position so as to permit the gate 30 to be slammed closed and latched without damaging any structural elements of the printing apparatus. Further, the latch assembly in accordance with the present invention is designed to minimize wear between contacting parts so as to maintain alignment of the frame 10 and gate 30 over long periods of use. In addition, however, any wear that does occur is inherently compensated for as a consequence of the latch assembly construction.

More particularly, in accordance with the present invention a latch assembly is provided which includes a male latch member in the form of a roller 40 mounted on the gate 30 for rotation about spindle 42. The roller 40 is preferably mounted at about the same level as the hammer tips 14 as shown in FIG. I. As is best shown in FIG. 2, the spindle 42 defines an axis of roller rotation which perpendicularly extends through the hinge axis of the gate 30.

The female member of the latch assembly includes a bracket 44 fixedly mounted on the hammer bank frame 10. More particularly, the bracket 44 includes a bight portion 46 which is secured to the frame by some fastener means such as appropriate bolts 48. Extending from the bight portion 46 is a lower leg 50 and an upper leg 52. The legs 50 and 52 extend substantially tangentially to an are described by the roller 40 when the gate 30 is pivoted about its hinge axis.

A receptacle 54 for the roller 40 is provided between the leg 50 and 52. That is, the receptacle is essentially defined by first and second perpendicular flat surfaces 56 and 58. The flat surface 56 defines a plane extending substantially perpendicular to the hinge axis of gate 30. The flat surface 58 is contiguous with and extends perpendicular to the flat surface 56. The inner surface of the leg 50 also defines an inclined entrance ramp 60 which leads to and is contiguous with the flat surface 56.

The wedge plate 64, (best illustrated in FIGS. 3 and 4) is secured to the leg 50 of bracket 44 for pivotal movement about pin 66. The wedge plate 64 is provided with a wedge surface 68 which has a radius curvature about point 70. It will be appreciated that as the wedge plate 64 is pivoted about pin 66, the distance between the wedge surface 68 and flat surface 58 of the bracket 44, considerably reduces. Thus, if the dimensions are appropriately selected, it will be appreciated that the wedge plate 64 can, when pivoted to the position illustrated in FIG. 4, wedge the roller 40 into the receptacle defined by flat surface 56 and 58. Thus, the position of the wedge plate illustrated in FIG. 4 is referred to as the latching position. When the wedge plate is pivoted to the position illustrated in FIG. 3, the roller 40 will of course not be latched in the receptacle. Thus, the position of the wedge plate illustrated in FIG. 3 is referred to as the unlatching position.

Whereas many prior art latch assemblies require that the latch elements be appropriately oriented before the gate can be slammed shut, one of the objects of the present invention is to permit the gate to be slammed shut and latched without damaging any of the structural features of the printing apparatus. In order to assure that the latch assembly elements of the present invention are always properly oriented, a pawl 76 is provided to cooperate with a step 78 formed in the wedge plate 64 adjacent the wedge surface 68. More particularly, the pawl 76 is mounted on the leg 52 of bracket 44 for pivotal movement about pin 80. The pin 80 is located so that when the pawl 76 is free hanging, it will engage the step 78 of wedge plate 64. The pawl 76 is also positioned in the path of movement of roller 40 so that as the roller 40 moves up the inclined ramp 60 and onto the flat surface 56, it will engage the pawl 76 and in turn move the pawl out of engagement with the step 78 and the wedge plate 64. As a consequence, the wedge plate 64 will then be free to pivot counterclockwise (as viewed in FIG. 4) to thus enable the wedge plate 64 to pivot from the unlatching position of FIG. 3 to the latching position of FIG. 4.

In order to assure the automatic movement of the wedge plate into the latching position when the pawl 76 is disengaged from the step 78, a spring 84 is provided which is coupled to a handle lever 90 which in turn is terminally coupled through a universal ball-and-socket-type joint to the outer face of the side panel of frame 10. Collar members 94 and 96 respectively coupled to the handle lever 90 and wedge plate 64 are connected by a turnbuckle 98 comprising a rod 100 having oppositely directed threads on the opposite extremities thereof.

In the operation of the latch assembly in accordance with the invention, initially consider the printing apparatus in the open position of FIG. 1. When the gate 30 is open relative to the hammer bank frame 10 the pawl 76 will be engaged with the step 78 in wedge plate 64 to thus hold the wedge plate in the unlatching position of FIG. 3. When the gate 30 is then slammed closed, the roller 40 will roll up the inclined entrance ramp 60 of bracket 44 onto the flat surface 56. It is emphasized that as a consequence of mounting the roller 40 for rotation about an axis extending through the hinge axis of the gate 30 and of orienting the inclined entrance ramp 60 substantially tangentially to an are described by the roller 40, the roller 40 will roll, rather than slide, up the entrance ramp 60. This arrangement substantially eliminates any sliding friction thereby considerably reducing wear as compared to prior art latch assemblies. By substantially eliminating wear, a latch assembly in accordance with the present invention can maintain precision alignment between the frame 10 and gate 30 over considerably longer periods of operation.

Returning now to the operation of the latch assembly, once the roller 40 emerges onto the flat surface 56, it will engage the pawl 76 to pivot it about pin to thus move the pawl 76 out of engagement with the step 78 of wedge plate 64 thereby permitting the spring 84 to pivot the wedge plate 64 to the latching position shown in FIG. 4. As a consequence of the shape of the wedge surface 68 of wedge plate 64, the wedge surface 68 will wedge or lock the roller 40 into engagement with the flat surface 58 of bracket 44. The dimensions of the wedge plate are selected so as to assure an appropriate wedge angle for locking the roller 40 into the receptacle against flat surface 58. It will be readily recognized by those skilled in the art that a minimum wedge angle for the particular wedge plate and roller materials involved can be detennined from appropriate mechanical engineering handbooks.

From the foregoing explanation of the operation of latch assembly, it will be recognized that in pivoting the wedge plate 64 to the latching position of FIG. 4, the spring 84 moves the handle lever in a counterclockwise direction as viewed in FIG. 4. In order to further assure that the drum 30 and frame 10 remain in the latched position, a detent plate 104 (FIG. 1) is provided to lock the handle lever 90 in a position corresponding to the latching position of the wedge plate. The detent plate ll04 is provided with an essentially vertically oriented slot 106. When the wedge plate 64 is in the unlatching position, the handle lever 90 will extend through the upper portion of the slot 106. When the spring 84 pulls the handle lever 90 downwardly to move the wedge plate 64 into the latching position, the handle lever 90 will extend through a lower portion of slot 106. In order to lock the handle lever 90 to prevent inadvertent unlatching of the wedge plate, the detent plate 104 is provided with a detent slot 108. That is, the handle lever 90 can be manually, laterally moved about joint 92 from the lower portion of the slot 106 into the detent slot 108. It will be appreciated, of course, that when the handle lever 90 extends through the detent slot 108, it cannot be inadvertently raised.

In order to move the wedge plate 64 to the unlatching position, it is necessary to manually move the handle lever out of the detent slot 108 of detent plate 104 and to the upper end of the slot 1106. This action will, of course, pivot the wedge plate 64 in a clockwise direction around pin 66, as received in FIG. 4. As the step 78 passes the pawl 76, the pawl will fall back into engagement with the step 78 to thereby automatically orient the wedge plate 64 so as to again permit the drum gate 30 to be slammed closed.

As a safety precaution, in order to assure that the drum 32 does not rotate when the gate 30 is open, a switch means is mounted on the outer face of the side panel of frame 10 so as to be actuated by the handle lever 90 only when the lever is in its locked position extending through detent slot 08. The printer electronics is also preferably controlled by a switch responsive to the handle lever position.

From the foregoing, it will be recognized that an improved latch assembly suitable for use in high-speed impact printers has been disclosed herein. The latch assembly is particularly suited for applications in which precision alignment between hinged members is required and where it is desired to minimize wear in order to assure continued alignment. Minimization of wear is accomplished by eliminating substantially all points of sliding friction. More significantly, sliding friction is eliminated by properly mounting the roller 40 with respect to the hinge axis of gate 30 and by projecting the entrance ramp 60 of bracket 44 substantially tangentially along an are described by the roller 40. Although wear has been substantially minimized, the utilization of a wedge plate inherently compensates for minimum amounts of wear. That is, as slight amounts of wear do occur, the wedge plate will merely pivot further to wedge the roller 40 against the surface 58 of the receptacle 54. Greater amounts of wear can be compensated for by adjustment of the turnbuckle 98.

It is still further pointed out that the latch assembly in accordance with the present invention automatically orients itself so as to enable the gate 30 to be slammed closed without causing any structural damage.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is: l. A latch assembly, useful in a high-speed impact printer, for latching and aligning first and second members pivotally coupled about a hinge axis, said assembly comprising:

a roller mounted on said first member for rotation about an axis extending perpendicularly through said hinge axis; I

a bracket fixedly mounted on said second member, said bracket including an inclined entrance ramp, extending substantially tangentially to an are described by said roller about said hinge axis, and leading to a first flat surface oriented perpendicular to said hinge axis; a wedge plate including a wedge surface; means mounting said wedge plate proximate to said bracket for pivotal movement about an axis lying in a plane oriented parallel to the plane of said first flat surface between latching and unlatching positions with said wedge surface respectively disposed to engage and be spaced from said roller on said first flat surface; pawl means for engaging said wedge plate to retain it in said unlatching position;

means mounting said pawl means adjacent to said first fiat surface and in the path of movement of said roller for enabling said roller to engage said pawl means to release said wedge plate; and

spring means coupled to said wedge plate acting to pivot said wedge plate toward said latching position.

2. The latch assembly of claim 1 wherein said bracket further includes a second flat surface contiguous with and extending perpendicular to said first flat surface remote from said entrance ramp; and wherein said wedge surface is spaced by a certain distance from said second flat surface when said wedge plate is in said unlatching position and is spaced by a distance considerably reduced from said certain distance when said wedge plate is in said latching position.

3. The latch assembly of claim 1 including a pivotally mounted handle lever;

means coupling said handle lever to said wedge plate for pivoting said wedge plate to said unlatching position; and

means for locking said handle lever with said wedge plate in said latching position.

4. The latch assembly of claim 3 including a switch means actuatable in response to said handle lever being locked.

5. A high-speed impact printer including:

a hammer bank frame;

a drum gate mounted on said frame for pivotal movement with respect thereto about a hinge axis;

a roller mounted on said drum gate for rotation about an axis extending substantially perpendicularly through said hinge axis;

a bracket fixedly mounted on said hammer bank frame, said bracket including an inclined entrance ramp extending substantially tangentially to an arc described by said roller about said hinge axis and leading to a first flat surface definrng a plane oriented substantially perpendicular to said hinge axis, said bracket further including a second flat surface contiguous with said first flat surface remote from said entrance ramp and extending substantially perpendicular to said first fiat surface; a wedge plate including a wedge surface; means mounting said wedge plate proximate to said first and second flat surfaces for pivotal movement about an axis lying in a plane oriented parallel to the plane of said first flat surface, between an unlatching position in which said wedge surface is spaced by a certain distance from said second flat surface and a latching position in which the spacing between said wedge surface and said second flat surface is considerably reduced from said certain distance;

pawl means for retaining said wedge plate in said unlatching position;

means mounting said pawl means adjacent said bracket in a position to be engaged and moved by said roller to release said wedge plate; and

spring means coupled to said wedge plate acting to pivot said wedge plate toward said latching position.

6. The printer of claim 5 including a drum carried on said drum gate and mounted for rotation about an axis; and wherein said roller axis of rotation and said drum axis of rotation lie in substantially a common plane oriented perpendicular to said hinge axis.

7. The printer of claim 5 including a pivotally mounted handle lever;

means coupling said handle lever to said wedge plate for pivoting said wedge plate to said unlatching position; and means for locking said handle lever with said wedge plate in said latching position.

8. The printer of claim 7 including a switch means actuatable in response to said handle lever being locked. 

1. A latch assembly, useful in a high-speed impact printer, for latching and aligning first and second members pivotally coupled about a hinge axis, said assembly comprising: a roller mounted on said first member for rotation about an axis extending perpendicularly through said hinge axis; a bracket fixedly mounted on said second member, said bracket including an inclined entrance ramp, extending substantially tangentially to an arc described by said roller about said hinge axis, and leading to a first fLat surface oriented perpendicular to said hinge axis; a wedge plate including a wedge surface; means mounting said wedge plate proximate to said bracket for pivotal movement about an axis lying in a plane oriented parallel to the plane of said first flat surface between latching and unlatching positions with said wedge surface respectively disposed to engage and be spaced from said roller on said first flat surface; pawl means for engaging said wedge plate to retain it in said unlatching position; means mounting said pawl means adjacent to said first flat surface and in the path of movement of said roller for enabling said roller to engage said pawl means to release said wedge plate; and spring means coupled to said wedge plate acting to pivot said wedge plate toward said latching position.
 2. The latch assembly of claim 1 wherein said bracket further includes a second flat surface contiguous with and extending perpendicular to said first flat surface remote from said entrance ramp; and wherein said wedge surface is spaced by a certain distance from said second flat surface when said wedge plate is in said unlatching position and is spaced by a distance considerably reduced from said certain distance when said wedge plate is in said latching position.
 3. The latch assembly of claim 1 including a pivotally mounted handle lever; means coupling said handle lever to said wedge plate for pivoting said wedge plate to said unlatching position; and means for locking said handle lever with said wedge plate in said latching position.
 4. The latch assembly of claim 3 including a switch means actuatable in response to said handle lever being locked.
 5. A high-speed impact printer including: a hammer bank frame; a drum gate mounted on said frame for pivotal movement with respect thereto about a hinge axis; a roller mounted on said drum gate for rotation about an axis extending substantially perpendicularly through said hinge axis; a bracket fixedly mounted on said hammer bank frame, said bracket including an inclined entrance ramp extending substantially tangentially to an arc described by said roller about said hinge axis and leading to a first flat surface defining a plane oriented substantially perpendicular to said hinge axis, said bracket further including a second flat surface contiguous with said first flat surface remote from said entrance ramp and extending substantially perpendicular to said first flat surface; a wedge plate including a wedge surface; means mounting said wedge plate proximate to said first and second flat surfaces for pivotal movement about an axis lying in a plane oriented parallel to the plane of said first flat surface, between an unlatching position in which said wedge surface is spaced by a certain distance from said second flat surface and a latching position in which the spacing between said wedge surface and said second flat surface is considerably reduced from said certain distance; pawl means for retaining said wedge plate in said unlatching position; means mounting said pawl means adjacent said bracket in a position to be engaged and moved by said roller to release said wedge plate; and spring means coupled to said wedge plate acting to pivot said wedge plate toward said latching position.
 6. The printer of claim 5 including a drum carried on said drum gate and mounted for rotation about an axis; and wherein said roller axis of rotation and said drum axis of rotation lie in substantially a common plane oriented perpendicular to said hinge axis.
 7. The printer of claim 5 including a pivotally mounted handle lever; means coupling said handle lever to said wedge plate for pivoting said wedge plate to said unlatching position; and means for locking said handle lever with said wedge plate in said latching position.
 8. The printer of claim 7 including a switch means actuatable in response to said handle lever being locked. 